Data storage devices that are connected via networks are used for safe storage of data prepared by a personal computer, etc. Such a network connected type data storage device is generally referred to as “NAS” (Network Attached Storage) and is widely used for backing up data and other applications due to enabling access from an arbitrary personal computer connected to networks and enabling handling with operability equivalent to a data storage process in a built-in disk drive device. Also in cases where the same data are to be used among a plurality of operators, cooperative work can be performed using the NAS as a storage site in common for the data.
In order to improve security and safety, U.S. Pat. No. 6,711,594 discloses a distributed data archiving device that can divide a single data file into a plurality of partition files and store these partition files respectively at different storage sites.
Though a general, conventional data storage system using network provides the merit of enabling data to be deposited and withdrawn from arbitrary terminal devices connected to networks, there is a limit to the physical storage capacity. Thus, when requests for storing large amounts of data are made from numerous terminal devices connected to the networks, situations may occur wherein the limit of the storage capacity is exceeded and the requests cannot be accommodated. Though as a countermeasure, hard disk devices and other hardware resources having adequate storage capacities can be secured in view of storage capacity demands that may arise in the future, it may not actually be possible to take adequate measures due to reasons of cost. Also, as a new problem of data storage devices using network, damages due to computer viruses have been increasing in recent years, and in cases where a stored data file is infected by a virus, unpredicted damage may spread via the networks.
An object of this invention is to provide a data storage system using network, with which the limits of storage capacity can be overcome as needed and yet with which damages due to computer viruses can be suppressed.